1. Field of the Invention
This invention relates to display devices.
In particular the invention relates to display devices which may be switched between light emitting and non-light emitting conditions.
2. Description of the Related Art
In U.S. Pat. No. 4,211,473 there is described a liquid crystal display device comprising a liquid crystal host material in which a pleochroic fluorescent dye is dissolved such that the molecules of the dye align with the molecules of the liquid crystal host material, the liquid crystal material being contained between two parallel glass plates, a reflector being arranged on one of these plates effective to reflect light incident on the reflector back through the device. By applying an electric field across the device effective to rotate the molecules of the liquid crystal host material, the amount of light absorbed by the dye through the plate which does not carry the reflector may be varied, the amount of fluorescence emitted by the dye, and thus the display varying correspondingly.
Such a display suffers the disadvantage however that the amount of fluorescence emitted by the dye will vary with the rotation of the dye molecules, and thus the applied electric field, according to a cosine law. Thus the variation of contrast of the display with applied electric field is gradual rather than sudden.